1. Field of the Invention
The present invention generally relates to a vehicle navigation system. More specifically, the present invention relates to a navigation method and system for providing routing information to a user based at least in part on traffic flow data and the availability of such traffic flow data.
2. Description of Related Art
Navigation systems for determining a route from a start point to a destination point are well known in the art. In addition, navigation systems having capabilities for determining the geographic position of a reference point are also well known in the art (e.g., a Global Positioning System (GPS) or a self-contained system having distance and bearing sensors). As an example, a commonly used navigation system allows a user (or driver) of a vehicle to enter a destination place into the navigation system. The navigation system then looks up an appropriate route from an original point (using its geographic positioning capabilities) to the destination point in a road map database (e.g., the route may be a route having the shortest distance from the start point to the destination, one which would take the vehicle the least time, or some other route), and guides the user to the destination point along the searched route through a visual display or vocal guide.
There are two general categories of traffic data/information: traffic flow data and traffic incident data. Ideally, both types of information would be available to a navigation device so that the navigation device can use the incident information to avoid a traffic incident and the flow information to avoid traffic congestion. In certain existing traffic information systems, traffic flow/speed data is collected at various points in a geographic region with flow/speed sensors. Data collected by the sensors are typically used to characterize traffic conditions on the roads in the region. Traffic flow information/data generally contains more information than traffic incident information, and is desirable to use in determining the optimal routes to a destination point. However, if traffic flow data is given undue weight or is not truly representative of traffic conditions on a route or a road link, routing calculations based on the traffic flow data can lead to erroneous vehicle routing information.
As a result, there remains a need for a method and system for selectively using traffic flow data to calculate one or more travel routes to a destination point. The method would preferably involve determining if traffic flow data coverage or availability level along one or more of the routes/links to the destination point is sufficient (i.e., at or above a predetermined coverage threshold level) before using the traffic flow data to calculate routing information, such as estimated time of arrival at the destination point. If the traffic flow data availability falls below the threshold level, it would be desirable to utilize an alternative route guidance technique to guide the vehicle to the destination point.
Accordingly, it would be desirable to provide a vehicle navigation method and system that overcomes the above-described shortcoming of the prior art while retaining their advantages.